Negative image silver transfer development

ABSTRACT

A gelatino-silver halide emulsion layer containing fogged silver halide crystals which have been treated with 5-nitrobenzimidazole is exposed to actinic radiation and processed by silver diffusion transfer development to give a negative image of an original on a receptor layer. Useful negative radiographic images can be obtained by the process.

United States Patent Blake [4 1 Mar. 14, 1972 [73] Assignee: E. I. du Pont de Nemours and Company,

Wilmington, Del.

May 21, 1969 [22] Filed:

[21] Appl. No.: 826,679

[58] Field of Search ..96/66, 29

[56] References Cited UNITED STATES PATENTS 2/1950 Stauffer ..96/64 3,464,822 9/1969 Blake Primary Examiner-David Klein Assistant Examiner-John L. Goodrow Attorney-James T. Corle [57] ABSTRACT A gelatino-silver halide emulsion layer containing fogged silver halide crystals which have been treated with 5 m nitrobenzimidamle is exposed to actinic radiation and processed by silver diffusion transfer development to give a negative image of an original on a receptor layer. Useful negative radiographic images can be obtained by the process.

4 Claims, No Drawings NEGATIVE IMAGE SILVER TRANSFER DEVELOPMENT BACKGROUND OF THE INVENTION This invention relates to photography and more particularly to preparation of images by the silver diffusion transfer process. Still more particularly it relates to the preparation of negative images by the silver diffusion transfer process.

The silver difiusion transfer process is well known in the photographic art. It forms the basis for the present day directpositive, print-forming cameras. However, the silver diffusion transfer process has hitherto been capable only of making positive copies of an original on a receptor layer. There was no way to prepare a negative image of an original by that process. The present invention teaches how to prepare a negative image by the silver diffusion transfer process.

SUMMARY OF THE INVENTION This invention uses a photosensitive layer comprising fogged silver halide crystals in a colloid binder. The fogged silver halide crystals are treated with S-nitrobenzimidazole at high pH to modify their solubility in the silver halide solvents used in silver diffusion transfer development. After the layer is exposed imagewise to actinic radiation, it is treated with an aqueous silver diffusion transfer developer and placed in contact with a receptor layer having nuclei for the deposition of metallic silver. A negative image of the original is obtained on the receptor layer and in the original photosensitive layer.

The gelatino-silver halide elements employed in this invention are those prepared by techniques known in the art. Silver chloride or chlorobromide emulsions may be used.

Useful receptor layers are those nonporous supports having nuclei deposited uniformly over the surface of the receptor for the deposition of metallic silver from the transfer developer solution. Useful receptor layers are described in US. Pat. No. 2,352,014.

Developers useful in practicing this invention are high pH 1- phenyl-3-pyrazolidone/hydroquinone developers containing 5-nitrobenzimidazole, 1-phenyl-5-mercaptotetrazole, and a silver halide solvent such as sodium thiosulfate.

The support for the emulsion layers used in this novel process may be any suitable web. For example, cellulose mixed esters, etc., may be used. Polymerized vinyl compounds, e.g., copolymerized vinyl acetate and vinyl chloride, polystyrene and polymerized acrylatcs may also be mentioned. The film formed from the polyesterification product of a dicarboxylic acid and a dihydric alcohol made according to the teachings of Alles, US. Pat. No. 2,779,684 and the patents referred to in the specification of that patent are suitable. Waterproof photographic paper base is also a suitable support.

ln a preferred embodiment of this invention a silver chlorobromide emulsion of low gelatin content coated on a support is fogged by exposure to white light, bathed in a solution of 5-nitrobenzimindazole, and dried in darkness. After the element is exposed imagewise, it is soaked in an aqueous silver transfer developer comprised of a high pH 3- pyrazolidone/hydroquinone developer, e.g., a 3- pyrazolidone/hydroguinone developer with added S-nitrobenzimidazole, l-phenyl-S-mercaptotetrazole, and thiosulfate ion. The element is then placed in contact with a silver ion transfer receptor layer such as that described in Rott U.S. Pat. Nos. 2,352,014 and Gray 2,878,121, Mar. 17, 1959, for seconds to several minutes. After the element and receptor are separated, a negative image is obtained on the receptor layer. Suitable 3-pyrazolidones are listed in Kendall US. Pat. No. 2,289,367, July 14, 1942.

The following example is intended to illustrate the invention without limiting its scope.

EXAMPLEl A photographic element was prepared by coating an aqueous gelatin dispersion of silver chlorobromide (20 mole percent silver chloride and 30 mole percent silver bromide) on a film base prepared as described in Example IV of Alles, US.

Pat. No. 2,779,684. The dispersion had a ratio of silver halide to gelatin of 19:1 by weight and was coated at a pH of 6 at a rate of I16 milligrams of silver halide per square decimeter. After drying, the element was bathed for 30 seconds in the following solution with white lights on:

[0 S-nitrobenzimidazole nitrate 25 ml.

solution (1 gram per 100 ml. ethanol) l.0 Molar Sodium hydroxide 25 ml.

The sample was rinsed 5 seconds, the white lights were extinguished, and the sample was dried. One-half of the sample was exposed to a No. 2A Photoflood Lamp for seconds at a distance of 1 foot. The exposed sample was soaked for 2 seconds in a developer of the following composition:

800 ml. 80 g. l6 g.

l g. 5.5 g. 2 g.

l0 ml.

g. I000 ml.

The emulsion side of the element was then placed in contact with the face side of a piece of Polaroid receptor paper. After 30 seconds, the sample and receptor were separated and both were washed in water for 1 minute and dried. The portion of the sample which received the second exposure was blackened and that portion of the receptor which had contacted the exposed portion of the sample was also blackened.

While gelatin is the preferred macromolecular waterpermeable organic colloid binder for the silver halide grains, mixtures of gelatin and dextran or dextrin can be used.

The process is useful for forming images of various types, and is particularly useful in forming negative radiographic images.

Suitable compounds for thiosulfate ions are sodium, potassium, and ammonium thiosulfate. Useful high pH transfer 3- pyrazolidone developers containing said compounds and other ingredients are described in Blake Ser. No. 401,971, filed Oct. 6, 1964, now US. Pat. No. 3,490,905. 5- Nitrobenzimidazole and l-Phenyl-S-mercaptotetrazole are added to the developer.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for forming a negative image in a receptor surface from an irnagewise exposed, prefogged, photographic gelatin-containing silver halide layer which comprises a. impregnating the layer with an aqueous solution of 5- nitrobenzimidazole,

b. impregnating the layer with an aqueous silver transfer developer of high pH containing a 3-pyrazolidone, hydroquinone, S-nitrobenzimidazole, l-phenyl-S-mercaptotetrazole, and thiosulfate ion,

0. placing the layer while wet in contact with the surface of a silver ion transfer receptor surface, and

d. separating the layers whereby a negative image is obtained on the receptor surface.

2. A process according to claim 1, wherein said gelatin is the sole binder for the silver halide.

3. A process according to claim 1, wherein the silver halide is silver chlorobromide.

4. A process according to claim 1, wherein said 3- pyrazolidone is l-phenyl-4-methyl-3-pyrazolidone.

i a l t i 

2. A process according to claim 1, wherein said gelatin is the sole binder for the silver halide.
 3. A process according to claim 1, wherein the silver halide is silver chlorobromide.
 4. A process according to claim 1, wherein said 3-pyrazolidone is 1-phenyl-4-methyl-3-pyrazolidone. 